Cassiopeia A is a supernova remnant: the tattered remains of a massive star that exploded. Astronomers estimate that light from the supernova would have reached Earth after the invention of the telescope, yet – mysteriously – history makes no mention of it.

Explore the science along with the scenery – Image Tours show Hubble pictures through an astronomer's eyes, pinpointing and explaining key features to add understanding to the joy of cosmic sightseeing.